The studies outline in this proposal are directed towards providing additional insights into the mechanism of cross-bridge force generation in muscle cells. Non-invasive laser diffraction methods, with an emphasis on the changes of the optical polarization properties upon the interaction of light with the muscle fiber, is the technique chosen. The complete characterization of the optical polarization property known as the technique of ellipsometry, provides for the determination of both the phase and the amplitudes of the electric field components after its interaction. The amplitude information specifically singles out the intrinsically anisotropic elements of the basic muscle structural unit, the sarcomere. As such, time evolution studies of the changes in amplitudes monitor the orientational and intrinsic dynamics of anisotropic elements within the sarcomere. Predominently, these are the myosin rods: light meromyosin and subfragment 2. Since this region of the sarcomeric structure is undetected by x-ray diffraction methods and unable to a labelled by extrinsic probes, the ellipsometry technique provides an important complementary link. The phase information provides additional information about the contractile apparatus. Here, the phase shift measured in ellipsometry experiments contains both intrinsic as well as form contributions. In this proposal, the method of separation of intrinsic and form information, using simultaneously obtained amplitude data, is outlined. This additional separation of contributing parts gives this method added advantage over the technique of transmission birefringence, which also contain both anisotropic and phase information, but is inseparable. The sequence of activity outlined in this proposal will focus on: skinned fibers studies; myosin extracted, subfragment I reconstituted systems; and intact fibers under isometric tetanus and quick release conditions.